Improved ventilation of areas of the lung and hence improved oxygen/carbon dioxide gas exchange in the blood circulation of the patient are brought about by the modulated alternating oscillation of the respiration pressure without increasing the basic level of the respiration pressure. This form of respiration is called high-frequency respiration, hereinafter called HF respiration for short. The physiological respiration of an adult is typically in the range of 9 to 18 breaths per minute, and this leads to a respiration rate of 0.15 Hz to 0.3 Hz. A premature or newborn baby breathes at a rate of 60 to 120 breaths per minute, which corresponds to a respiration rate of 1 Hz to 2 Hz. The modulated frequency of high-frequency respiration, hereinafter called HF frequency, is in the range of 5 to 20 oscillations per second, i.e., markedly above the physiological respiration rates. At the outlet of the HF respirator, the HF respiration continuously generates oscillations of the pressure amplitude, which follow the HF frequency, which are superimposed to a physiological alternation of inspiration and expiration and a mean airway pressure. The HF frequency, the mean airway pressure, the pressure amplitude of the HF oscillation and the I:E (Inspiratory:Expiratory) ratio, which corresponds to the ratio of the duration of inspiration to the duration of expiration, are sent as input parameters to a control and regulating unit for controlling and regulating the mode of operation of HF respiration.
This input parameter comprising the frequency, pressure amplitude, mean airway pressure and I:E ratio is derived by the user from therapeutic considerations and the patient's constitution and can be set by the user as direct set points on an operating unit, on the one hand, and, in another variant, the set points can also be derived from other parameters. A process of how the HF frequency and the pressure amplitude of the HF oscillation can be derived from a set tidal volume is described in DE 102006048680 B3. WO 2007142642 A1 describes a process for controlling pressure fluctuations at the rhythm of a modulated HF frequency for a respirator. A respirator for use of the HF respiration is described in DE 3417954 A1, wherein a sine-like alternating pressure amplitude is admitted to the patient feed line in the rhythm of the HF frequency by means of a generator in conjunction with a valve arrangement and a negative alternating pressure amplitude is generated by means of a suction nozzle by actively drawing out the expiration air. The patient feed line connects the respirator to the patient, into whose lungs the pressure change oscillation is then introduced by means of an endotracheal tube or a breathing mask. The control and regulating unit converts the input parameters HF frequency, mean airway pressure, pressure amplitude and I:E ratio into the necessary manipulated variables for the pressure and flow regulation and actuation of the components of the device, for example, the suction nozzle and the valve arrangement. To generate a pneumatic pressure change oscillation at the patient, an air volume must be displaced through the patient feed line towards the patient and then away again. The patient feed line represents a dynamic pneumatic resistance for the amount of air fed, which resistance can be described by a low-pass filter. It results from this that to send a pressure change oscillation to the patient with increasing frequency, the flow velocities necessary for this increase superproportionally.
To avoid additional pneumatic resistances and volumes in the gas feed line at the patient's mouth and pressure drops resulting therefrom, sensor systems located near the patient for detecting the flow rate are dispensed within HF respiration in many cases. To adequately provide diverse possibilities of combination of variation of the pneumatic parameters, e.g., resistance and compliance, for different types of patients and different tube systems, with the HF respiration, the HF respirator is operated with excess gas volume and with a flow velocity resulting therefrom in order to ensure the intended and set pressure change amplitude and HF frequency at the patient in all cases. Due to this operation with gas excess, the metered quantity of gas is greater than is necessary for the respiration settings.